The present invention generally relates to materials used for the fabrication of structural members. More specifically, the present invention relates to processing chemically treated wood products and wood waste from wood biomass from forest or wood industries and fabricating such products and waste, along with waste thermoplastic, into useful structural members. These chemically treated wood products, wood waste and waste thermoplastic otherwise must be disposed, which is expensive and/or difficult.
Many wooden materials used as structural members must be chemically treated to render the wood suitable for the particular use or purpose. For example, wooden poles, posts and cross-members used for supporting utility lines, railroad cross-ties, and signs are usually pressure treated with creosote oil, which acts as a fungicide, germicide and insecticide to protect those members from various forms of fungal, bacterial and insect attack. Other chemicals are used to accomplish these purposes.
The benefits of chemically treated wooden structural members are well documented. For example, the life expectancy for untreated railroad ties installed during 1900 was four to six years. However, the life expectancy for ties treated with coal tar creosote is approximately thirty years. Nevertheless, because of the tremendous amount of railroad track in service, railroads in the a railroad tie remains relatively short because the ties are subject to substantial compressional and impact stresses as train cars travel over the rails. Because the pressure treatment does not penetrate the entire matrix of a wooden structural member, cracking of the outside structure can provide a pathway for water and microorganisms to invade untreated wood within the tie. The wood ultimately rots and deteriorates under train traffic. These same types of problems exist for other creosote treated wooden members which, according to the particular use, experience various types of environmental exposure and are subject to dynamic loading and the related stresses. Because these members have a limited life span, there is an ongoing demand for these structural members for application in both new and existing installations. The demand is aggravated by diminishing natural resources, including the hardwood from which most of these products are manufactured.
In addition to a supply shortage, an additional problem exists regarding chemically treated wooden members. Because a tremendous number of these members must be replaced each year, disposal is required for the removed members. However, because of the chemical treatment of these members with creosote oil and other substances that have been classified as hazardous substances, disposal of these items can be difficult and expensive. Various solutions have been proposed for disposal of the chemically treated wood as opposed to landfill disposal. Railroad crossties are commonly used for building retaining walls, raised gardens and other landscaping projects. Another proposed solution is to reduce the wooden members to mulch like material and use the material as fuel in wood fired boilers to generate electricity. There have also been proposals for recycling the wooden members to be reused for the same purpose. While these proposals seemingly solve two problems at once, to date none have widely been accepted. Part of the problem is that transporting the used materials for processing is itself prohibitively expensive. Regarding recycling members, the known processes result in a laminated final product that raises concerns about the integrity of the member at the layer boundaries.
In addition to disposing of chemically treated wooden structures, disposal of plastic structures and plastic waste is an ongoing problem. Plastic structures and plastic waste can be bulky and consume valuable landfill space. Although the recycling of plastics has been increasing, depending upon the particular application, some plastics are not acceptable.
The disclosed structural members solve the above problems. The disclosed process for manufacturing the structural members may be located on site or located immediately adjacent to a railroad siding, thereby eliminating or greatly reducing the transportation costs of other methods. The disclosed structural members may have no layering but rather have a uniform matrix. The disclosed process uses recycled thermoplastics to fabricate the disclosed structural members, thereby having the added benefit of providing an alternative used for plastics which might otherwise be discarded.